Backgrounds:

Few data are published on immune responses against SARS-CoV-2 induced by COVID-19 vaccines in people under the age of 18 years compared with adults.

Methods:

COV006 is a phase 1/2, single-blind, randomised controlled trial of ChAdOx1 nCoV-19 (ChAd) in children and adolescents aged 6-17 years in the UK. Participants were randomised 4:1:4:1 to receive two doses of ChAd or control (capsular group B meningococcal) vaccine (4:1), 28 days (short-interval) or 84 days (long-interval) apart. The primary outcome was safety and tolerability, with immunogenicity in the baseline-seronegative participants as the secondary outcome. Due to the restrictions in the use of ChAd introduced during the study, only participants aged 12-17 years randomised to the short-interval were vaccinated as planned (D28). The remaining participants received their second dose at D112.

Results:

Of 262 participants, 211 and 51 were randomised to the ChAd and control arms, respectively. No serious adverse events related to ChAd administration were recorded. Solicited adverse reactions were reported more frequently after the first dose compared with the second dose, across all age and interval groups.

In participants aged 12-17 years, anti-SARS-CoV-2 IgG and pseudoneutralising antibody titres at D28 post-second dose were higher in the long-interval arm (geometric mean ratios (GMR): 1.70, 95%CI: 1.27-2.26 and 1.99, 95%CI: 1.39-2.86, respectively) than after a short-interval.

Humoral responses were higher in participants aged 6-11 years than those aged 12-17 years (GMR: 1.48, 95%CI: 1.07-2.07 and 2.96, 95%CI: 1.89-4.62 for anti-SARS-CoV-2 IgG and pseudoneutralising antibody titres, respectively). Cellular responses peaked after a first dose of ChAd across all age and interval groups.

Conclusions/Learning Points:

ChAdOx1 nCoV-19 is well-tolerated and immunogenic in children aged 6-17 years. No safety concerns were raised in this trial.